TGR5 (also known as G protein-coupled bile acid receptor 1 (GPBAR1), M-BAR, or BG-371) is a receptor present on L-cells within the gastrointestinal compartment in humans. Upon binding of bile acids, TGR5 causes the release of glucagon-like peptide-1 (GLP-1) which in turn stimulates insulin secretion and suppresses glucagon secretion (Katsuma et al., Biochem. Biophys. Res. Commun., 2005, 329 (1), 386-390). Therapeutic attempts have been made to elevate GLP-1 in the blood to improve glycemic control. One approach involves the use of dipeptidyl peptidase-4 (DPP-4) inhibitors to slow down GLP-1 degradation. Another approach employs GLP-1 analogs that mimic the natural GLP-1. Yet another approach utilizes TGR5 agonists to stimulate the TGR5 receptor and trigger its signal cascades within the L-cells for glucose control.
Multiple TGR5 modulators with diverse structural features have been reported. U.S. Pat. No. 8,114,862 discloses a series of 23-substituted bile acids that mimic natural bile acids as TGR5 modulators. WO2013/164838 discloses TGR5 agonists containing 1, 2, 4-triazole with a linker containing sulfur and their use in treating diabetes, obesity and related disorders. WO2009/026241 discloses TGR5 modulators having a structure of pyrimidin-4-one that is fused with a 5 or 6-membered heterocyclic or heteroaryl group. WO2012/082947 discloses pyrazolyl based TGR5 agonists. WO2011/071565 discloses TGR5 agonists that are imidazole derivatives. WO2012/149236 discloses bicyclic heteroaryl compounds that are TGR5 agonists. WO2013/134527 discloses polycyclic alkaloids as TGR5 agonists. WO2004/067008 discloses TGR5 agonists containing benzodiazepine-2-one. WO2013/096771 discloses TGR5 agonists containing tetrahydroquinoxaline and their use in treating type 2 diabetes mellitus. WO2013/096771 further discloses some TGR5 compounds that are substantially non-bioavailable in the blood stream.
There has been a concern for an increased risk of pancreatitis in type 2 diabetes patients treated with GLP-1-based therapies (Singh et al., JAMA Intern. Med., 2013, 173 (7), 534-539). Subsequent clinical studies, however, do not seem to support this contention (Butler et al., Diabetes, 2013, 62 (7), 2595-2604). It remains to be determined if systemic delivery of a TGR5 agonist may attribute to the pancreatitis.
Phillips et al. disclosed trifluoromethyl(pyrimidin-2-yl)azetidine-2-carboxamides as potent, orally bioavailable TGR5 agonists (J. Med. Chem., 2014, 57(8), 3263-3282). The lead Compound (45h) represents a potent and selective TGR5 agonist that has high plasma exposure (i.e., high Cmax value). The authors reported glycemic effect of Compound 45h was lost upon chronic dosing. Phillips et al. questioned toxicological and therapeutic issues that may limit the utility of these systemic TGR5 agonists for treatment of metabolic disease.
There is a continuing need in developing a non-systemic TGR5 agonist, one that is restricted in the gastrointestinal compartment and has clinical safety and efficacy profiles suitable for oral administration in treating metabolic disorders.